One important aspect of livestock farming involves the treatment of the animals with insecticides and other substances. Proper care requires that certain treatments, particularly insecticide spraying, be done on a regular basis due to the limited effective lifetime of the substance applied as affected by natural chemical degradation of the substance and by the dilution or washing away of the substance through rain, mud or the washing of the animals. Application of insecticide and other such substances is commonly accomplished by rounding up the livestock and spraying with a hand-held sprayer, which job is time consuming and even worse unpleasant. Accordingly, there are available a number of automatic spraying systems and devices, as demonstrated by the prior art.
U.S. Pat. No. 3,032,011 to Stramel; U.S. Pat. No. 3,173,402 to Cassel; U.S. Pat. No. 3,870,023 to Wilson; and U.S. Pat. No. 4,334,504 to Matthews all disclose automatic livestock spraying apparatus for spraying a liquid insecticide over the body of an animal. In the case of U.S. '402 to Cassel a relatively complicated apparatus is provided to utilize the weight of an animal to pressurize the insecticide to be sprayed, and to utilize the movement of an animal through the device to release the pressurized insecticide in spray form at the appropriate time. The relative complexity of that apparatus makes it undesireable from both a cost and maintenance viewpoint. In the case of U.S. '011 to Stramel a somewhat simpler apparatus is provided in which a pressurized tank is provided to hold liquid insecticide, which is directed through a valve to spray nozzle. The valve is operated through a linkage including a trip mechanism which when displaced by an animal moving its head into a salt lick container, opens the valve to permit pressurized insecticide to be sprayed over the animal's body. While somewhat simpler then the Cassel apparatus, the Stramel apparatus does not provide for a uniform metered dose of insecticide to be sprayed over the animal, and thus can result in either too little or too much insecticide being applied per treatment. The apparatus of U.S. '504 to Matthews discloses another pressurized liquid insecticide system utilizing an insecticide valving system wherein the valve is opened by an animal, in this case the body of the animal as it passes by the spraying apparatus. Like the Stramel apparatus, the Matthews apparatus relies on the somewhat erratic movement of the animal to both activate and deactivate the spraying apparatus such that a uniform dose of insecticide treatment is not assured.
U.S. '023 to Wilson does, however, disclose apparatus which provides for the application of a uniform dose of insecticide to an animal. The Wilson system includes an electrical pump and time delay circuit for this purpose, requiring a battery or other source of energy. In the case where batteries are utilized it is thus necessary to change or recharge them on a regular basis, or in the case of A.C. power a line must be run to the spraying device, either of which requirements are less than ideal. Moreover, electronic components of delay circuits are to some extent temperature sensitive such that fluctuations in the ambient temperature may effect the operation of the device, and are also subject to corrosion of the contacts, another source of malfunction. Moreover, electrical components of the system are relatively expensive as compared to for instance, the simpler mechanical valving apparatus of Matthews or Stramel.